FIG. 3 shows the arrangement of a conventional wire cut type electric discharge machine. In FIG. 3, reference numeral 1 designates a workpiece; 2, a movable table on which the workpiece 1 is mounted; 3, a wire cut type electric discharge machine body (hereinafter referred to merely as "a machine body 3", when applicable); 4, a wire electrode used for machining the workpiece 1; a machining solution supplying device for supplying a machining solution to a gap formed between the wire electrode 4 and the workpiece 1; 6, a numerical control device for performing a position control operation and a machining control operation in the machine body 3, an automatic wire-break return operation of the wire electrode 4, and so forth (hereinafter referred to as an NC device 6", when applicable); 7, an automatic wire electrode supplying device for automatically connecting or cutting the wire electrode 4; and 8, a machining power source device for supplying discharge current to the machining gap between the wire electrode 4 and the workpiece 1.
FIG. 4 is a block diagram showing the arrangement of the NC device in detail. In FIG. 4, reference numeral 9 designates an NC program for controlling the machine body 3; 10, a program analyzing section for analyzing the NC program 9; 11, a machining solution control section for controlling the machining solution supplying device 5 to supply the machining solution to the machining gap; 12, an automatic supply control section for controlling the automatic wire electrode supplying device 7 to automatically connect or cut the wire electrode 4; 13, a wire control section for controlling the feed of the wire electrode 4 or outputting a wire break signal; 14, machine input/output section for transmitting signals to or receiving signals from the machining solution controlling section 11, the automatic supply controlling section 12, and the wire controlling section 13; and 15, a control unit. The control unit 15 drives a servo motor 16 according to an output signal of the program analyzing section 10 to control the position of the movable table 1, and applies signals through the machine input/output section 14 to the machining solution control section 11, the automatic supply control section 12 and the wire control section 13 to control the supply of the machining solution, the feed of the wire electrode 4 and the machining operation. Furthermore, when the wire electrode 4 is broken, in response to the wire break signal from the wire control section 13, the control unit 15 performs controls to automatically return the wire electrode 4.
Further in FIG. 4, reference numeral 17 designates a display section for displaying data such as coordinates on a CRT (cathode ray tube) 18; and 19, a machining skip data storing table into which, when the present configuration machining operation is skipped over to the next configuration machining operation for instance because of the breakage of the lo wire electrode 4 during discharge machining, data on the machining start position of the configuration machining operation which has been suspended, namely, machining start hole coordinates or machining start hole number is stored through the control unit 15.
The above-described machining skip is controlled entirely by the control unit 15.
FIG. 5 is a diagram for a description of a finish machining operation. In FIG. 5, reference character (a) designates a rough machining path; (b), a finish machining path; (c), a machining start hole; and (d), a machining end hole.
FIG. 6 is a flow chart for a description of the finish machining operation.
FIG. 7 shows a case where a plurality of finish machining operations are given to workpiece.
FIG. 8 is a diagram showing the occurrence of a machining skip.
FIG. 9 is a flow chart for a description of the occurrence of a machining skip.
The operation of the electric discharge machine thus constructed will be described with reference to FIG. 7.
First, at the machining start hole (A), the automatic wire electrode supplying device 7 is operated to automatically connect the wire electrode 4. The workpiece 1 is not machined yet, and rough machining electrical conditions are set. A machining operation is carried out along the rough machining path (a) to the machining end point (B) with machining current supplied from the machining power source device 8.
At the machining end point (B), the automatic wire electrode supplying device 7 is operated to automatically cut the wire electrode 4. The wire electrode 4 is moved along a path (d) to the machining start hole (D) of the second rough machining path (a.sub.1). At the machining start hole (D), similarly as in the above-described case, the wire electrode 4 is automatically connected. Under the rough machining electrical conditions, a machining operation is carried out along the rough machining path (a.sub.1) to the machining end point (E).
Similarly, a machining operation is carried out along the next rough machining path (a.sub.2). Thus, the three rough machining operations have been accomplished.
Thereafter, the wire electrode 4 is moved to the machining start hole A again, where it is automatically connected.
Now, a finish machining operation will be described with reference to a flow chart of FIG. 6.
First, for a finish machining operation, in Step 20 the electrical conditions are changed to finish machining conditions, the amount of offset of the wire electrode 4 with respect to the workpiece 1 is changed, and the number of times of finish machining, namely, looping frequency is set, for instance, to one (I).
In Step 21, machining configurations are read out.
According to the machining configurations thus read out, a finish machining operation is carried out from the machining start hole (A) to the machining end point (G) in the same process as in the above-described rough machining operation; that is, the finish machining operation is carried out along the rough machining paths (a), (a.sub.1) and (a.sub.2) in a manner as shown in FIG. 5. Thus, the finish machining operation has been achieved for the three machining configurations.
In the above-described finish machining process, the machining operation is carried out twice including the rough and finish machining operations. However, the number of times of machining should be determined according to the surface roughness which is to be given to the workpiece 1.
In the above-described machining operations, it is determined whether or not a machining operation is to be continued, as shown in FIG. 9. In Step 24, it is determined whether or not a configuration machining operation is carried out according to the NC program. When it is determined that the configuration machining operation is carried out according to the NC program, then Step 25 is effected. In Step 25, it is determined whether or not a fault occurs during machining such as the breakage of the wire electrode or the short-circuiting of the wire electrode 4 and the workpiece 1. If no such fault occurs, the machining operation is continued as indicated in Step 26. If such a fault occurs, then it is determined that it is impossible to continue the machining operation, as a result of which Step 27 is effected. In Step 27, data on the machining start position of the configuration machining operation which cannot be continued; i.e., machining skip data such as the machining start hole coordinates or machining start hole number are stored in the machining skip data storing table 19 shown in FIG. 4. Furthermore, the configuration machining operation is suspended, and then the movable table 2 is moved until the wire electrode 4 is moved to the machining start hole of the second configuration machining operation. Under this condition, the second configuration machining operation is carried out.
The machining skip data stored in the machining skip data storing table 19 are displayed on the CRT 18 so as to warn the operator attracting his attention.
The conventional wire cut type electric discharge machine thus constructed is disadvantageous in the following points: For instance, in the case where, when rough machining operations are carried out as shown in FIG. 7, a machining skip occurs with the workpiece 1 during the first rough machining operation and a finishing machining operation is performed to the workpiece 1, it is necessary for the operator to confirm the contents of the machining skip data storing table 19 which are displayed on the CRT 18, to suspend the first configuration machining operation and to shift the latter to the second configuration machining operation. If, without confirmation of the contents of the table, a finish machining operation has been given to the first configuration, then finish machining operations will be given to the remaining configurations which have not been rough-machined yet. In this case, the workpiece thus machine is low in configuration accuracy and not uniform in surface roughness.